The London Stock Exchange (LSE) was forced to suspend morning trading on one of its two share trading platforms for almost two hours on Tuesday amid fears that a rival had sabotaged its systems.
The LSE said it was investigating the "suspicious" glitch that delayed its year-long attempt to switch securities to a faster new trading system. The LSE's Turquoise trading platform remained shut until 10.30am on Monday.
Later, an LSE spokeswoman admitted that the "human error" behind the glitch may have occurred in "suspicious circumstances".
Last month, the stock exchange operator delayed switching stocks on its main market to the new MillenniumIT system to allow further network upgrades, but has now been forced to abandon any updates until next year.
The LSE had planned the move as the new system makes trading faster and more attractive for high-frequency trading firms that generate huge volumes.